Melt the butter in a heavy-bottomed saucepan over medium heat. Cook the shallots until soft and translucent, about 3 minutes. Pour in the water and peas, season to taste with salt and pepper. Increase the heat to medium-high, bring to a boil, then reduce heat to low, cover, and simmer until the peas are tender, 12 to 18 minutes.
Puree the peas in a blender or food processor in batches. Strain back into the saucepan, stir in the cream if using, and reheat. Season to taste with salt and pepper before serving.
